Waterproof paper and process of making same



Patented Oct. 1931 UNITED STATES PATENT OFFICE LESTER KIRSOHBRAUN, F LEONIA, NEW JERSEY, ASSIGNOR TO THE FLINTKOTE COMI- PANY, OF BOSTON, 'MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS WATERPROOF PAPER AND PROCESS OF MAKING SAME No Drawing. Application filed May 13,

This invention relates to a method of producing Waterproof felted fibrous sheets wherein the fibrous constituents are combined with the waterproofing ingredients prior to the felting operation. More particularly the invention is concerned with a method of producing waterproof felted sheets wherein normally non-fluid and adhesive bitumens are employed as the waterproofing ingredients, these materials, .when properly associated with the fibers, providing very efiective barriers against the entrance or permeation of water into the sheet.

In order to combine normally adhesive waterproofing material, such as asphalt or the like, with fibers prior to a felting operation for forming the several constituents into felted sheets, the waterproofing material must first be rendered relatively non-adhesive in order to prevent gumming up of the blankets and other parts of the paper machine. Methods of thus converting the relatively adhesive waterproofing material, as for example, asphalt, to a relatively non-adhesive condition, and sheeting a mixture thereof with fibers on a paper-making machine, are described in Patent No. 1,536,399 issued to me May 5, 1925. In accordance with said patcut, the asphalt or other bituminous or pitchy binder, is brought to a relatively non-adhesive state, as for example, by emulsifying the same in an aqueous medium comprising an emulsifying agent and water, whereupon the emulsified bituminous binder is mixed with fibrous pulp and amalgamated uniformly therewith, as for instance, in the beater or in the stuff chest, and is then run off in the usual manner on the paper-making machine. The non-adhesive character of the emulsified bitumen enables the paper forming operation to be carried on witnout gumming the blankets or other parts of the machine, due to the fact that this characteristic prevails as long as the emulsion is stable and highly resistant to pressure during the sheet forming operation, which condition, as soon as substantially complete elimination of water from the sheet occurs, (e. g. on the driers), permits the dispersed bitumen particles to coalesce and resume their adhesive character, resulting in 1929. Serial No. 362,877.

the union thereof with and about the fibers so as to produce a highly water-resistant sheet.

The present invention has for its chief object the provision of a process of producing waterproof felted sheets quite similar to the process above referred to and more particularly set forth in the said patent. According to the present invention, the transformation of the waterproofing material to a condition as above described whereby to render possible the admixture thereof with fibres and the fabrication of such mixture on a paper machine, is achieved in the heaters usually employed to reduce the fibrous material to pulpy condition suitable for passage over the paper forming mechanism so that the beating or equivalent agitating mechanism transforms the binder to a condition in which it is uniformly distributed therethrough. I have further found that most fibres that are employed commercially in paper manufacture possess colloidal properties when beaten out for a substantial length of time, and that this colloidal nature of the pulp can be utilized. as a means for assisting in the dissemination of bituminous material such as asphalt throughout the pulp stock for assisting in converting the same to condition permitting the same to be manipulated successfully over the paper machine. The efficiency of the fibrous pulp in this regard may be further assisted by means of the addition of suitable protective colloids, and in practical operation of the process herein described, suitable proportions of protective colloid are employed to insure against any tendency of the bitumen to adhere to the paper makinginstrumentalities.

In carrying out the invention the desired fibrous material is introduced into a beater with suflicient quantities of water to permit circulation therein, and while the mass of fibers is being beaten therein, or after it has been beaten out to a sufficient extent, the bituminous binder, as for example, asphalt of 100 to 200 F. melting point in heat liquefied state, is fed gradually to the beater while the stock is approximately at or somewhat above the melting point of the asphalt and the 0peration of the beater is continued for a sufficient time to effect uniform distribution of the bitumen throughout thepulp, I have found that the pulpy fibrous mass 1s capable, under the continued action of the beater roll, of acting upon the heat liquefied b tumen to produce a state of intimate association of the bitumen with the fibres,in the aqueous content of the mass.

In some instances it may be found neces sary or desirable to assist in the distribution of the bitumen through the pulpy mass by incorporating therein, either before the 1ntroduction of the bitumen or simultaneously therewith, suitable quantities of colloidal material, as for example, colloidal clay, finely powdered mineral oxides, gelatine, tannlc acid and starch. The amount of colloidal material thus incorporated will be regulated in accordance with the hardness of bitumen used in the process, (the latter depending largely upon the hardness desired in the final product), the amount of bitumen to be combined with the pulp, and the character of the fibrous pulp, particularly its own ability to effect subdivision of the bitumen and cause the latter to assume a relatively non-adhesive condition. Thus, where the proportions of ingredients in the beater are such that the bitumen comprises 20 to 70% thereof on the dry weight basis, and with Mexican asphalt of a melting point of 150 to 170 F., the transformation of the asphalt to a non-adhesive condition may be assisted, if necessary, by the addition of 1 to 5% of colloidal clay, on the basis of weight of asphalt. The protective colloid serves also to ensure against sticking of the asphalt to the blankets or other parts I of the machine.

In actual practice, even where the bitumen may be distributed in the pulp as above described, small amounts of protective colloid should be incorporated in the mass in order to increase the stability of the dispersed material against the pressure and mechanical action to which it is subjected in passing over the paper machine and to insure against any tendency of the dispersed material to adhere to the various parts of the machine. For this purpose the protective colloid in suitablequantities may be added to the beaten mass of pulp and bitumen after the latter has been fairly completely distributed through the pulp by the beating action in the presence of the pulp, or, if desired, the colloid may be introduced before or simultaneously with the introduction of the bitumen. In any event,

however, the quantities of protective colloid will be governed by the factors above noted and by the inherent relative stability of the dispersion effected by means of the fibrous pulp itself. Generally, however, with materials and proportions as above stated, 2 to, 8% of clay, bentonite or similar colloid will suflice to make the operation practical from all points of view.

After the bitumen combined with the pulp in the beater, has been converted to the requisite non-adhesive condition and stabilized, if necessary, in the manner described, the mixture is in readiness for the sheeting operation. In order to cause the dispersed bitumen particles to clot or deposit upon the fibers and'provide a freely-felting furnish, alum, preferably in the presence of sodium, or other alkali silicate, may be added at any convenient stage prior to the passage of the mixture over the forming screen. The alum should be employed in sufficient quantities to flocculate or precipitate any unattached bitumen onto the fiber, so that the water will run clear from the stock during formation. The action of the alum upon the soluble silicate or other reacting substances present produces a voluminous bulky precipitate, which acts as a further protective film interposing itself between the bitumen and any contacting parts of the apparatus. In practice 3% silicate and 5% alum will be sufiicient to produce the result and bring the stock to an acidic condition. The wet web of felted fibrous material with its contained bituminous binder is capable of passing over the various parts of the paper machine, by virtue of the fact that the relatively non-adhesive condition of the stock is preserved until the water is substantially completely removed. As the last portions of water are removed in the passage of the sheet over the driers, the bitumen regains its normally adhesive character and fuses to coalesce and form more or less continuous filn'ls about the fibers.

While I have described the operation as applied to a single web, it is obvious that the features of the invention may be utilized in connection with one or more cylinders of a multi-cylinder machine. Thus, the adhesive binder may be combined with fibrous stock of certain of the plies (for example, the inner ply or plies), while the fibrous stock of the other (outer) plies may be left free of the bituminous binder. The invention is alsoadaptable for wet-board machine operation, in which case the bituminous binder rendered non-adhesive as-above described, is contained in the fibrous stock of the cylinder mould, so that as the successive layers are transferred fromthe blankets to the make-up roll, the composite structure will be permeated throughout with the binder in relatively nonadhesive condition.

Having thus described my invention, what I claim is:

1. In the process of making a felted waterresistant sheet on a paper making machine, the steps which comprise subjecting fibrous material in an aqueous vehicle to the action of a heater to thereby produce a fibrous pulp, introducing into said pulp a normally adhesive, fusible, waterproof binder in heat liquefied condition, effecting agitation of said binder in the presence of said pulp whereby to distribute the binder substantially uniformly through the pulp, adding regulated quantities of a protective colloid to the stock of pulp and bitumen to stabilize the bitumen and prevent sticking thereof to the paperforming instrumentalities, running off the stock on the paper-making machine, and finally removing the water from the stock to cause the bitumen to regain its adhesive character and coalesce and unite with the fibers.

2. In the process of making a felted waterresistant sheet on a paper-making machine, the steps which comprise subjecting fibrous material in an aqueous vehicle to the action of a beater to thereby produce a fibrous pulp, introducing into said pulp a normally adhesive, fusible, Waterproof binder in heat liquefied condition, effecting agitation of said binder in the presence of said pulp, whereby to distribute the binder substantially uniformly through the pulp, adding regulated quantities of a mineral powdered protective colloid to the stock of pulp and bitumen to stabilize the bitumen and prevent sticking thereof to the paper-forming instrumentalities, runnng off the stock on the paper-making machine, and finally removing the water from the stock to cause the bitumen to regain its adhesive character and coalesce and unite with the fibers.

3. In the process of making a felted waterresistant sheet on a paper making machine, the steps which comprise subjecting fibrous material in an aqueous vehicle to the action of a beater to thereby produce a fibrous pulp of colloidal characteristics, introducing into said pulp a normally adhesive, fusible,

waterproof binder in heat liquefied condition, effecting agitation of said binder in the presence of said pulp whereby to distribute the binder uniformly through the pulp, adding regulated quantities of a clay-like protective colloid to the stock of pulp and bitumen to stabilize the bitumen and prevent sticking thereof to the paper-forming instrumentalities, running off the stock on the paper-making machine, and finally removing the water from the stock to cause the bitumen to regain its adhesive character and coalesce and unite with the fibers.

4. In the process of making a felted water-resistant sheet on a paper-making machine, the step-s which comprise introducing 'a normally adhesive, fusible, water-proof binder in heated liquid condition, into a mass of fibrous material, agitating the mass to effect distribution of the binder substantially uniformly through the pulp, adding regulated quantities of a protective colloid to the stock of pulp and binder to stabilize the bitumen and prevent the sticking thereof to the paper forming instrumentalities, running off the stock on a paper-making machine, and finally removing the water from the stock to cause the bitumen to fuse and coalesce so as to form continuous films about the fibers.

5. In the process of making a felted waterresistant sheet on a paper-making machine, the steps which comprise introducing a normally adhesive, fusible, water-proof binder in heated liquid condition, into a mass of fibrous material, agitating the mass to effect distribution of the binder substant' ally uniformly through the pulp, adding regulated quantities of a protective colloid to the stock of pulp and binder to stabilize the bitumen and prevent the sticking thereof to the paper forming instrumentalities, adding alumto the stock to cause the bitumen to clot or deposit upon the fibers and provide a freely feltable furnish and running off the stock on a paper-making machine.

In testimony whereof I affix my signature.

LESTER KIRSCIIBRAUN. 

